(a) Field of the Invention
The present invention relates to an air temperature conditioning control apparatus for controlling environmental conditions within a supermarket or such commercial store having large refrigeration requirements, and more specifically to the control of latent loads occurring in such stores and imposed upon open refrigerated display fixtures. The fixtures have open refrigerated display zones separated from the conditioned room space by one or more planes (curtains) of refrigerated air, which is substantially lower in temperature than the conditioned room space and which absorb energy from the room air adjacent these planes causing the room air to be cooled. The apparatus of the invention comprises an air handling housing having a return air chamber and a make-up air chamber isolated from the return air chamber. Each of the chambers has an outlet connected to a mixing compartment for mixing the conditioned air from the chambers at their outlets. Air moving means is connected to the mixing compartment for displacing the conditioned air, via convection ducts, back into the space. Each of the chambers further has an inlet, a filter section and a cooling section. The inlet of the return air chamber is supplied primarily with air cooled by the refrigerated display fixtures. The space is maintained at a substantially constant temperature throughout and is substantially unaffected by air cooled by the refrigerated fixtures. In other words, the refrigerating effect of the display fixtures upon the room air being returned to the air handling package constitutes the primary air tempering or cooling means in the entire system, but the refrigerated fixtures have no direct effect upon the room space in which they are located.
(b) Description of Prior Art
It is a well known fact that environmental control in a supermarket is affected by forces and conditions that do not normally occur in any other commercial, industrial or residential structure. These are the forces and conditions imposed on the space by the refrigeration equipment inherent in any modern supermarket. For example, a 25,000 square foot supermarket may have open display refrigeration fixtures requiring a refrigeration capacity of as much as 50 tons (600,000 BTU/HR) with a range of evaporator temperatures from -35.degree. F. to +25.degree. F. This inexorable cooling force exists without regard to the needs of the conditioned space. As a result, unless special emphasis is given to design of the environmental control apparatus and system, the conditioned space experiences a wide variety of undesirable conditions such as cold aisles, over cooling in areas of heavy display case concentrations, under cooling (warm spots) in areas where there are no display fixtures, extreme stratification of air (the temperature gradient between floor and ceiling may be as much as 35.degree. F.), and control of the environment's latent heat loads is near impossible. The specific moisture content of the air in the conditioned space is usually a function of outside air conditions, but relative humidity varies considerably because of variations in air temperature throughout the space.
Refrigeration compressors in a supermarket account for approximately 44% of the total supermarket energy consumption at design conditions. Increases in dry bulb temperature above design conditions have no affect on the compressor load and its energy usage as long as the wet bulb in the conditioned space remains constant. Conversely, with constant dry bulb temperatures, variations in wet bulb temperature (and therefore relative humidity) have a dramatic affect on the compressor's load, and therefore the energy consumed. Increases in the wet bulb temperature result in load and energy increases, while decreases in wet bulb temperature result in decreases in load and energy consumption.
The refrigeration effect induced by the display fixtures upon the environment must therefore be controlled. This, however, must influence the design of the building, the calculation of environmental loads, both cooling and heating, and design of the apparatus. In the example of the 600,000 BTU/HR refrigeration load, approximately 75% or 450,000 BTU/HR could represent a direct refrigerating effect by the display fixtures upon the conditioned space. This massive refrigerating effect is a potential source of cooling that can be credited against the space environmental cooling loads providing steps are taken in design of the system, and apparatus to absorb, treat and redistribute this refrigerating effect. Thus, absorption and use of this refrigerating effect produces conditions which dictate very special design considerations in the requirements of the air cooling and conditioning apparatus.
The refrigerating effect of the supermarket display fixtures has an unusual affect upon the environment's latent heat loads. There are, basically, two components of latent load which must be considered; the internal latent load derived from sources within the conditioned space such as people and appliances (coffee urns, steam tables, etc.), and ventilation latent load which is a function of the fresh make-up air supplied to the conditioned space from the outside or ambient environment. The latent component of the refrigerating effect from the display fixtures acts directly upon the internal latent load. This is to say that that portion of the internal latent heat load equal to the latent component of the refrigerating effect is directly absorbed by the display fixture cooling coils. This, again, produces an unusual condition which must be taken into consideration in design of the conditioning apparatus. Since the internal latent load is acted upon directly by the display fixtures, the ventilation latent load is left as a dominant latent load and in the interest of energy efficiency, this too dictates the need for special consideration in the design of the conditioning apparatus.
Recovery of the heat rejection from the supermarket's refrigeration systems is likewise important, both to the control of environmental conditions and to the control of energy input. Heat reclaimer systems, per se, are well known in the industry and in practice have been applied to the recirculated supply air stream, downstream of the air conditioning cooling coil in the apparatus where waste heat from the refrigeration systems can be employed as a reheat medium for humidity control, when required, as well as a heat source for store heating during periods when heating, as opposed to air conditioning, is required for environmental control.
In this position in the conventional conditioning control apparatus, the heat reclaim coil is exposed to extreme variations in entering air temperature resulting from the mixing of outside make-up air with return air from the conditioned space. This, together with extreme variations in display fixture loads, which occur with normal changes in atmospheric conditions, create serious operational problems in the refrigeration systems whereby the condensing temperatures of the refrigeration systems are reduced below satisfactory operating levels or massive quantities of refrigerant are required for condensing temperature/pressure control in the systems.